THERE is something Garbo-esque about Stef Penney. Maybe it is because she has unusually vivid blue eyes, long, slender bones and enviable cheekbones set in a luminous face that is all intriguing planes and angles. Mainly, though, it's her spiky persona, which she wears like so much metaphorical barbed wire.
The air of mystery she exudes only adds to her resemblance to the Hollywood star who so famously wanted to be left alone.
Indeed, when the Edinburgh-born-and-bred novelist, who is hotly tipped to be one of the literary talents of 2007, arrives at the East End cafe where we meet in London, she is wearing impenetrable Garbo-style dark glasses, even though it's a wintry day starved of sunlight.
She removes the glasses when she sits down, but over the next 90 minutes she might just as well have gone on wearing them, since she rarely makes eye contact and is infuriatingly evasive.
Does she live alone in her Hackney flat? "No." With her partner? "No, I don't have a partner." Does she share with friends or family? "No." But she does not live alone? "No, I don't live alone." Aha, so she lives with her fictitious characters then? "Whatever. You can say anything you want. I've vowed never to read anything anyone ever writes about me anyway," she says, fiercely balling up the remains of her pain au chocolat in a napkin.
Only minutes into meeting her and I feel as if I am sitting opposite a passive-aggressive clam.
However, I will forgive Penney for all her obfuscation and prickly unwillingness to divulge anything about herself because she has made a remarkable literary debut. Her brilliantly assured, subtly written novel, The Tenderness of Wolves, set in the atmospheric icy wastes of 19th-century Canada and published to admiring reviews last autumn, is surely a dead cert to win the First Novel category in the Costa Coffee chain's sponsorship of the awards formerly known as the Whitbreads.
Divided into five categories, they are worth 5,000 each. The winners will be announced on 10 January - and I confidently predict that Penney will walk away with the First Novel prize. If she doesn't, there is no justice. The winner of the 25,000 prize will be named on 7 February. What makes Penney's achievement so astonishing, however, is the fact that she is a recovering agoraphobic, who has battled cripplingly violent panic attacks for the past 12 years, ever since she left Bristol University, where she read philosophy and religion, before studying film and TV at Bournemouth College of Art and being selected on graduation for the Carlton Television New Writers Scheme.
Agoraphobia is not a fear of open spaces, as is commonly believed, but acute anxiety about situations where escape would be difficult, she points out. For Penney, that meant any form of travel was indescribably frightening and it took her two-and-half years to master the London buses so that she could make the 20-minute bus ride from her home to the British Library to research her book.
The Tenderness of Wolves is ostensibly about a murder hunt, although it's also an epic adventure and a poignant love story. The bloody body of a trapper is found by his clear-eyed neighbour, Mrs Ross, whose 17-year-old son is also missing. With the enigmatic William Parker, she sets off across the frozen tundra in search of the boy.
So convincingly and brilliantly has Penney conjured this unforgiving landscape that people tell her they find it impossible to believe that she has never been there, that she has never trekked across the vast, snow-bound outback, which is her idea of hell anyway, although she says she finds snow and ice "seductive and terrifying in equal measure".
When her novel was sold in Canada earlier this year, they refused to believe that she was not one of them, although the closest she has been to a frozen wilderness was on desolate holidays in the Highlands as a child, when she recalls miserably trudging through mud.
She was in her twenties when her first panic attack struck, while she was squashed into the back of a car. From then on, any form of travel would trigger another terrifying attack. "They were horrific," she says.
She knew they were not physically dangerous. Nonetheless, she felt as though she was going to die. "The best way I can describe it is as a massive, unexpected blow to the kidneys - my faculties of reason would shut down, my body would lock into a foetal crouch and I wouldn't be able to move until it passed.
"This would be accompanied by a racing heart, hyperventilating, sweating, crying and a feeling of utter dread."
Her greatest fear was of the bewildering panic itself: "It's simply the most frightening thing I've ever experienced". She became fascinated by what would have happened to someone like her in the 19th century, before the age of therapy and safe sedatives. She knew she would have sought help wherever she could have found it and so the idea of Mrs Ross, a character addicted to laudanum as a result of panic attacks, was born.
She first appeared in Penney's first screenplay, about the Highland Clearances, Nova Scotia, which is to be filmed by Hawick-born producer Margaret Matheson's Bard Entertainments company. Hettie MacDonald will direct the film and the role of Mrs Ross has been offered to "someone we are desperate to get". Surely, it's Tilda Swinton? Penney looks sphinxlike, saying only that she so fell in love with the character and her husband Angus that she couldn't bear to let them go, hence the novel.
When we meet Mrs Ross in The Tenderness of Wolves, she is "clean", but still showing agoraphobic symptoms. "The one thing I knew was that she was going to go on a journey, and that journey would be incredibly hard for her as a result." Penney has learnt how to manage her own agoraphobia, after trying all sorts of therapy - individual, group, behavioural ("a total waste of time"), hypnotherapy, flying courses, drugs. Finally, she says, she got so sick of her own limitations she had to find the courage to overcome them. "But I don't think I'll ever be 'normal' again - if there is such a thing."
Is she thrilled to have made the shortlist for the biggest literary prize in Britain, apart from the Man Booker? Wrapping her long fingers around a mug of milky coffee, she shudders: "It's scary. Very, very scary. It puts enormous pressure on me for the second novel, which I'm working on. Also, it means that people want bits of me now and I'm not prepared to give them."
She mimes hands plucking at her. "I was told that I should talk about my agoraphobia, because another writer on the list is a cancer sufferer [Michael Cox, who won a 500,000 advance for his Victorian-set drama The Meaning of Night, and who is losing his sight due to the disease]. To be honest, I couldn't care less about publicity and I'm certainly not going down that my-life's-a-misery route."
Unfortunately, I tell her, when you sign a contract to publish a novel you can't tick the no-publicity box - unless you are J D Salinger, say, or Harper Lee. "But I'm not interesting. My life's boring," she responds. "I write. End of story. It's one of the few jobs relatively unaffected by travel foibles, so it's the perfect career for an agoraphobic."
Somewhere in her mid-thirties - she testily refuses to reveal her age, saying she thinks it's ridiculous that newspapers insist on putting ages in brackets after names - Penney is a screenwriter of some note. She's written and directed two films: 10 x 10, starring Anna Friel, "as an agoraphobic woman - ha! ha!", for the BBC, and The Knowledge, a bizarre take on an adulterous relationship, featuring Lucy Russell, which was selected for the Film Council's 2002 Digital Shorts season. In addition, she has written screenplays for another dozen films. But it is as an acclaimed novelist that she finds herself walking backwards into the limelight. "I sold a book. That does not mean that I sold myself," says the younger of two daughters of a librarian mother and a businessman turned arts fund-raiser, although Joe Penney is now retired. Her parents still live in the capital, but she refuses to talk about them, saying only that she was "a difficult child". They lived in Glasgow for a while "when I was a kid", and then came back to live in south Edinburgh, where she was educated. "I hated school. No, I won't say which one. My English teachers told me I couldn't write, because I had no imagination. That's the sort of school it was and that's all you need to know. Anyway, I couldn't wait to get away from Edinburgh because I loathed it. I always wanted to live in London, which I love," she says, playing with the crumbs of her breakfast. Recently, she got on a plane for the first time in years. She flew to Lapland to research a screenplay set in the Arctic. "It was terrifying, but I did it. I've also been to Finland. Once we were up there, looking down on the clouds that looked like a vast plain of snow, I found I was enjoying it. Losing something, then finding it again, is an incredible rush.
"It's taken me a long time," she sighs. "But I've finally reclaimed my freedom."
• TEN years of First Novel winners under the Whitbread awards:
2005: THE HARMONY SILK FACTORY by Tash Aw
2004: EVE GREEN by Susan Fletcher
2003 VERNON GOD LITTLE by DBC Pierre
2002 THE SONG OF NAMES by Norman Lebrecht
2001 SOMETHING LIKE A HOUSE by Sid Smith
2000 WHITE TEETH by Zadie Smith, below
1999 WHITE CITY BLUE by Tim Lott
1998 THE LAST KING OF SCOTLAND by Giles Foden
1997 THE VENTRILOQUIST'S TALE by Pauline Melville
1996 THE DEBT TO PLEASURE by John Lanchester